1. Field of the Invention
The invention relates to a cooling system for the leading-edge region of a hollow gas-turbine blade, in which a duct, through which flow occurs longitudinally, extends from the blade root up to the blade tip and is defined in the region of the blade body on the one hand by the inner walls of the leading edge, the suction side and the pressure side and on the other hand by a web connecting the pressure side to the suction side, the inner walls of the suction side and the pressure side being provided with a plurality of ribs, which run slantwise and at least approximately in parallel, and the suction-side ribs and the pressure-side ribs being offset from one another over the blade height.
The invention therefore relates very generally to a system for cooling a curved wall, around which hot medium flows on one side and a cooling medium flows on its other side.
2. Discussion of Background
Hollow, internally cooled turbine blades with liquid, steam or air as cooling medium are sufficiently known. In particular, the cooling of the leading-edge region of such blades poses a problem.
DE-C2 32 48 162 discloses a cooling system of the aforementioned type. The inner walls of the region considered are equipped with ribs, which run radially outward from the leading edge right up to the web. These ribs have a height which at each point is between 10% and 33% of the local height of the cooling-medium duct. Thus the leading-edge region is supposed to be effectively cooled even in the case of a narrow duct. Here, the ribs are provided in order to initiate and encourage turbulence, and the cooling fluid is said to be directed through the blade without great resistance. Vortices which have a velocity component toward the leading edge are supposed to develop due to the slanting arrangement of the ribs in a defined direction. This is supposed to lead to the cooling medium being deflected as a body toward the leading-edge region, whereby this region is effectively cooled even without film cooling. To this end, the actual leading edge is constructed so as to be free of ribs. On the inside, it has a cylindrical shape with a radius which corresponds approximately to the height of the adjoining ribs. The distance of the ribs from the leading edge is between one to five times the rib height.
Further considerations as to how the heat transfer can be improved by means of ribs in so-called triangular ducts--as represented by the leading-edge region of a gas-turbine blade--are set forth in the Journal of Thermophysics and Heat Transfer, Vol. 8, No. 3, July-September 1994, on pages 574-579 in an article by Zhang et al.
However, the problem with the triangular ducts equipped with ribs of the same height is that, due to the large cross section at the base of the triangle, an excessive quantity of cooling medium flows through there as a result of the lower resistance, a fact which may lead to the shortcomings mentioned below.